Method and device for monitoring moisture related operating condition of an immersed solid dielectric material

ABSTRACT

A method and device for monitoring, within an enclosure, moisture content level of a solid dielectric material, or paper, immersed in a dielectric fluid, or oil, both of which having respective moisture content, and known water solubility properties varying with temperature, and a corresponding bubble formation temperature. The device includes a moisture detector and a temperature detector for measuring the oil moisture content and temperature levels, respectively. A microprocessor, electrically connected to both the moisture and the temperature detectors, has the known water solubility properties of the paper and the oil stored therein along with the oil gas content level and the enclosure pressure related data and processes the oil moisture content level and the oil temperature level so as to determine the paper moisture content level and the bubble temperature. The latter being displayed on a display connected to the microprocessor.

CROSS-REFERENCE TO RELATED APPLICATION

[0001] The present application is a Continuation-In-Part (C.l.P.) ofpending U.S. patent application Ser. No. 10/194,265 filed on Jul. 15,2002.

FIELD OF THE INVENTION

[0002] The present invention relates to the field of sensing devices andis more particularly concerned with a method and a device for monitoringthe moisture related operating condition of a solid dielectric materialimmersed in a dielectric fluid used in power transformers and oil-filledpower cables.

BACKGROUND OF THE INVENTION

[0003] As it is well-known in the art of high voltage transformers, themoisture content of the paper insulation used to insulate the wires inthe windings affects the insulation characteristic of the transformer,the higher the moisture content is the lower its insulatingcharacteristic is. High moisture content reduces the electricalresistance of the insulation which promotes local heating, especiallyduring emergency overloading of the transformer, and increases theoccurrences of small discharges that tend to degrade even further thepaper insulation. Therefore, high moisture content shortens theinsulation life duration.

[0004] It is also well known that the moisture content generallyincreases over time, mainly due to paper aging, infiltration andinspection. This increase of moisture content in the paper insulationforces the transformer to have a decreasing overload capacity over time.

[0005] The moisture content level of the paper insulation can beevaluated and/or estimated through the measurement of the moisturecontent level of the oil in which the windings, including the paperinsulation, is immersed in. It is relatively easy to measure themoisture content of the oil since a lot of such devices are available inthe market. Once the oil moisture content is known it is somewhattedious to go through the analysis process in order to estimate thepaper moisture content in different locations of the transformer.Accordingly, in practice, no one ever does or sees the necessity to dosuch an analytical estimation.

[0006] U.S. Pat. No. 5,343,045 granted to Gupta on Aug. 30, 1994,discloses a method and device for measuring moisture content of anabsorbent material such as paper insulation in transformers. The devicedirectly measures the humidity/moisture level in the absorbent materialusing an optical technique. The technique requires an end of an opticfiber to be installed almost in contact with the absorbent material orpaper insulation.

[0007] Since the device provides a local direct measurement, ispreferably located at a critical area of the transformer. Such acritical area is not always easily accessible and may require a somewhatcomplex and expensive installation of the device on the transformer.Furthermore, the location of such a critical area is not really knownfor sure and changes with the transformer loading. In order to get ageneral overview of the paper moisture content in the differentlocations of the transformer, either a plurality of devices or acalculated estimation is required. Notwithstanding the fact that such adevice may provide reliability problems over time, especially problemsassociated with the maintaining of a proper position of the opticalprobe in proximity to the absorbent material.

[0008] The drawbacks associated with the prior art devices is theirinability to provide an operator/user with a constant monitoring of themoisture level of the paper insulation using relatively simple andwell-known temperature and humidity sensors. Furthermore, the assessmentof the paper moisture content for different locations in the transformeris never performed due to its complexity. Nevertheless, such anassessment could prove to be beneficial over time in order tosignificantly increase the lifetime of the transformers as well as theircontinuous use at a substantially higher maximum overload capacitycompared to their usual derated overload capacity required to compensatefor all of the unmonitored behaviors thereof, for safety reasons.

[0009] Accordingly, there is a real need for an improved method anddevice -for monitoring the moisture level of an immersed soliddielectric material.

[0010] Furthermore, an oil dryer-filter connected to the transformer isgenerally used to extract water from the oil. When such a filter becomessaturated in water, its efficiency is considerably reduced, if not null,and could affect the overload capacity of the transformer until it isreplaced or cleaned up. Although the oil filters are generally providedwith a known water extraction capacity, they sometimes lose efficiencybefore reaching their extraction capacity, which is bad for thetransformer.

[0011] Accordingly, there is a need for continuously monitoring theproper functioning of the oil dryer-filter during operation of the highpower transformer.

[0012] Furthermore, bubble evolution from overloading of a transformeris a concern due to possible dielectric failure. Since overloading isinevitable for short periods during peak demand periods, it is necessaryto specify the limits of overloading with respect to winding hot spottemperature, which determines bubble evolution such as the temperatureat which bubbles will start to be formed.

[0013] Accordingly, there is a need for continuously monitoring thebubble temperature evolution of an immersed solid dielectric materialduring operation of a power transformer of the like.

SUMMARY OF THE INVENTION

[0014] It is therefore a general object of the present invention toprovide an improved method and device for monitoring moisture relatedoperating condition of a solid dielectric material immersed in adielectric fluid of a power transformer, a oil-filled power cable andthe like.

[0015] An advantage of the present invention is that the method and/ordevice for monitoring moisture related operating condition of animmersed solid dielectric material provide a relatively accurateestimate.

[0016] A further advantage of the present invention is that the methodand/or device for monitoring moisture related operating condition of animmersed solid dielectric material to provide an estimate for differentlocations inside the transformer.

[0017] Yet another advantage of the present invention is that the devicefor monitoring moisture related operating condition of an immersed soliddielectric material is relatively stable over time.

[0018] Still another advantage of the present invention is that thedevice for monitoring moisture related operating condition of animmersed solid dielectric material operates over very large temperatureand pressure ranges.

[0019] Still a further advantage of the present invention is that thedevice for monitoring moisture related operating condition of animmersed solid dielectric material can be easily installed orretrofitted on existing transformers, at accessible locations.

[0020] Another advantage of the present invention is that the methodand/or device for monitoring moisture related operating condition of animmersed solid dielectric material are not affected by the presence ofcontaminants within the dielectric fluid.

[0021] A further advantage of the present invention is that the methodand/or device for monitoring moisture related operating condition of animmersed solid dielectric material can be adapted by the user for use indifferent dielectric fluids and/or for different types of soliddielectric materials.

[0022] Still another advantage of the present invention is that themethod and/or device for monitoring moisture related operating conditionof an immersed solid dielectric material can provide all sorts of usefulinformation concerning the status, or health, of the transformer(s).

[0023] Furthermore, the use of moisture detectors located upstream anddownstream of the oil dryer-filter (any type of oil dryer apparatus,including vacuum type apparatus) used to extract water from the oilallows for continuous monitoring of the proper functioning of the oilfilter; the upstream moisture detector is preferably simultaneously usedfor the monitoring of the moisture content in the immersed soliddielectric.

[0024] Another advantage of the present invention is that the methodand/or device for monitoring operation of a fluid dryer-filter calculatethe rate of water extraction as well as the total amount of waterextracted from the transformer oil and paper since the beginning of thedry out procedure and the water accumulated in the filters since thelast filter cleaning or replacement (not applicable with vacuum-typewater extraction).

[0025] A further advantage of the present invention is that the methodand/or device for monitoring moisture related operating condition of animmersed solid dielectric material provide for the bubble temperatureevolution within a transformer during operation thereof.

[0026] According to an aspect of the present invention, there isprovided a device for monitoring moisture content level of a soliddielectric material inside an enclosure and a corresponding bubbleformation temperature within the enclosure, said solid dielectricmaterial being immersed in a dielectric fluid, said dielectric fluidfilling said enclosure, said solid dielectric material and saiddielectric fluid having a respective moisture content, said soliddielectric material and said dielectric fluid having known watersolubility properties varying with temperature thereof, said dielectricfluid having a gas content level thereof, said enclosure having pressurerelated data thereof, said device comprises:

[0027] a moisture measuring means for measuring moisture content levelof said dielectric fluid;

[0028] a temperature measuring means for measuring temperature level ofsaid dielectric fluid; and

[0029] an electronic circuit means for computing said moisture contentlevel of said solid dielectric material and said corresponding bubbleformation temperature, said electronic circuit means being electricallyconnected to both said moisture measuring means and said temperaturemeasuring means, said electronic circuit means having said known watersolubility properties of said solid dielectric material and saiddielectric fluid stored therein, said electronic circuit meansprocessing said fluid moisture content level and said fluid temperaturelevel so as to determine said solid dielectric material moisture contentlevel and said bubble formation temperature using said solid dielectricmaterial moisture content level, the dielectric fluid gas content leveland the enclosure pressure related data.

[0030] Typically, the electronic circuit means includes a displayingmeans for displaying said solid dielectric material moisture contentlevel and said corresponding bubble formation temperature, saiddisplaying means being electrically connected to said electronic circuitmeans.

[0031] Typically, the device includes an operator interfacing means foran operator to interface with said electronic circuit means, saidoperator interfacing means being electrically connected to saidelectronic circuit means so as to allow said known water solubilityproperties of said solid dielectric material and said dielectric fluid,the dielectric fluid gas content level and the enclosure pressurerelated data to be provided to and stored in said electronic circuitmeans.

[0032] In one embodiment, the electronic circuit means is remotelyelectrically connected to both said moisture measuring means and saidtemperature measuring means so as to allow said moisture measuring meansand said temperature measuring means to be located in a generallyinaccessible location.

[0033] In one embodiment, the device includes an operator interfacingmeans for an operator to interface with said electronic circuit means,said operator interfacing means being electrically connected to saidelectronic circuit means, said electronic circuit means providing asensor location menu through said operator interfacing means so as toallow an operator to select a specific location of both said moisturemeasuring means and said temperature measuring means within saidenclosure, whereby said specific location affecting determination ofsaid solid dielectric material- moisture content level and saidcorresponding bubble formation temperature by said electronic circuitmeans.

[0034] In one embodiment, the device includes:

[0035] a second moisture measuring means for measuring second moisturecontent level of said dielectric fluid, said electronic circuit meanscomparing said first and second dielectric fluid moisture content levelsand calculating a relative difference therebetween relative to saidfirst dielectric fluid moisture content level, said electronic circuitmeans displaying on said displaying means either a warning message whensaid relative difference is equal or larger than a predetermined valueor said solid dielectric material moisture content level and saidcorresponding bubble formation temperature when said relative differenceis smaller than said predetermined value;

[0036] whereby said second moisture measuring means being a referencemoisture measuring means to enable detection of malfunction of saiddevice.

[0037] In one embodiment, the device includes:

[0038] a second temperature measuring means for measuring secondmoisture temperature level of said dielectric fluid, said electroniccircuit means processing said first and second fluid temperature levelsand said fluid moisture content level so as to determine first andsecond solid dielectric material moisture content levels respectively,said electronic circuit means displaying on said displaying means anaverage of said first and second solid dielectric material moisturecontent levels and said corresponding bubble formation temperature.

[0039] Typically, the first and second temperature measuring means arelocated adjacent bottom and top regions of the enclosure, respectively.

[0040] Alternatively, the device includes:

[0041] a second moisture measuring means for measuring second moisturecontent level of said dielectric fluid, said electronic circuit meanscomparing said first and second dielectric fluid moisture content levelsand calculating a relative difference therebetween relative to saidfirst dielectric fluid moisture content level, said electronic circuitmeans processing said first and second fluid moisture content levels andsaid fluid temperature level so as to determine first and second soliddielectric material moisture content levels respectively, saidelectronic circuit means displaying on said displaying means either awarning message when said relative difference is equal or larger than apredetermined value or an average of said first and second soliddielectric material moisture content levels and said correspondingbubble formation temperature when said relative difference is smallerthan said predetermined value;

[0042] whereby said second moisture measuring means being at least areference moisture measuring means to enable detection of malfunction ofsaid device.

[0043] Typically, the pressure related data includes a pressure levelwithin the enclosure, and wherein said device further includes apressure measuring means for measuring pressure level within theenclosure, said electronic circuit means being electrically connected tosaid pressure measuring means.

[0044] According to another aspect of the present invention, there isprovided a method for monitoring moisture content level of a soliddielectric material inside an enclosure and a corresponding bubbleformation temperature within the enclosure, said solid dielectricmaterial being immersed in a dielectric fluid, said dielectric fluidfilling said enclosure, said solid dielectric material and saiddielectric fluid having a respective moisture content, said soliddielectric material and said dielectric fluid having known watersolubility properties varying with temperature thereof, said dielectricfluid having a gas content level thereof, said enclosure having pressurerelated data thereof, said method comprising the following steps:

[0045] a) measuring moisture content level of said dielectric fluidusing a moisture detector;

[0046] b) measuring temperature level of said dielectric fluid using atemperature detector; and

[0047] c) computing said solid dielectric material moisture contentlevel and said corresponding bubble formation temperature using aprocessor electronic circuit, said electronic circuit being electricallyconnected to both said moisture detector and said temperature detector,said electronic circuit having said known water solubility properties ofsaid solid dielectric material and said dielectric fluid stored therein,said electronic circuit processing said fluid moisture content level andsaid fluid temperature level so as to determine said solid dielectricmaterial moisture content level and said bubble formation temperatureusing said solid dielectric material moisture content level, thedielectric fluid gas content level and the enclosure pressure relateddata.

[0048] Typically, the method includes the step of:

[0049] d) displaying said solid dielectric material moisture level andsaid corresponding bubble formation temperature using a display, saiddisplay being electrically connected to said electronic circuit toreceive said solid dielectric material moisture content level and saidcorresponding bubble formation temperature therefrom.

[0050] In one embodiment, step b) includes measuring a second moisturecontent level of said dielectric fluid using a second moisture detector;step c) includes said electronic circuit processing said first andsecond fluid temperature levels and said fluid moisture content level soas to determine first and second solid dielectric material moisturecontent levels respectively; and step d) includes displaying on saiddisplay an average of said first and second solid dielectric materialmoisture content levels and said corresponding bubble formationtemperature.

[0051] Typically, the first and second temperature detectors are locatedadjacent bottom and top regions of the enclosure, respectively.

[0052] Other objects and advantages of the present invention will becomeapparent from a careful reading of the detailed description providedherein, within appropriate reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0053] In the annexed drawings, like reference characters indicate likeelements throughout.

[0054]FIG. 1 is a schematic diagram illustrating a device for monitoringthe moisture related operating condition of an immersed solid dielectricmaterial in accordance with an embodiment of the present invention, thesolid dielectric material of the illustration being the insulation paperused in a high power transformer;

[0055]FIG. 2 is a schematic flow diagram showing a method for monitoringthe moisture related operating condition of an immersed solid dielectricmaterial in accordance with an embodiment of the present invention;

[0056]FIG. 2a is a schematic flow diagram similar to FIG. 2, showing amethod for monitoring the moisture related operating condition inaccordance with another embodiment of the present invention;

[0057]FIG. 3 is a diagram similar to FIG. 1, illustrating otherlocations for the moisture detectors of the embodiment of FIG. 1,upstream and downstream of an oil dryer-filter unit fluidly connected tothe high power transformer; and

[0058]FIG. 4 is a schematic flow diagram showing the monitoring of thefunctioning of the oil dryer-filter unit of FIG. 3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0059] With reference to the annexed drawings the preferred embodimentsof the present invention will be herein described for indicative purposeand by no means as of limitation.

[0060] Referring to FIG. 1, there is shown a schematic diagram of adevice 10 for monitoring moisture related operating condition of a soliddielectric material 12 in accordance with an embodiment of the presentinvention, such as monitoring moisture content of the solid dielectricmaterial 12 immersed in a dielectric fluid 14 inside an enclosure 16 andthe corresponding bubble formation temperature within the enclosure 16.The dielectric fluid 14 generally entirely submerges the soliddielectric material 12. The solid dielectric material 12 and thedielectric fluid 14 have a respective moisture content, and each hasknown water solubility properties varying with their respectivetemperature. The dielectric fluid 14 has a gas content level thereofthat takes into account all gases dissolved therein. The enclosure 16has pressure related data associated therewith, such as the enclosureheight (from top to bottom), the pressure level therein (or atmosphericpressure for a non-sealed type enclosure) and the enclosure altitude.Although the following description, schematically illustrated in FIG. 1,is generally focused on the solid dielectric material being theinsulation paper 12 used to insulate the windings W of high powertransformers immersed in oil 14, any other similar application such asoil-filled power cables and the like could alternatively be consideredwithout departing from the scope of the present invention. Arepresentative alternate application is the insulation paper wrappedaround high power transmission cables immersed in oil and generallyrunning under water and/or under ground.

[0061] The device 10 includes a probe 18 preferably comprising first andsecond oil temperature measuring means, or detectors 20, 20 a, and afirst and a second oil moisture measuring means, or detector 22, 22 a tomeasure the temperature level and first and second moisture contentlevels of the oil 14 of the transformer, respectively. The second oiltemperature detector 20 a and the second oil moisture detector 22 a aremainly used as a validation and/or calibration detectors as explainedhereinafter.

[0062] Preferably, the moisture detectors 22, 22 a are capacitance-typemoisture sensors well known in the art since they are substantiallyrelatively stable over time (years), not affected by the presence ofcontaminants within the dielectric fluid 14 and operate over very largetemperature and pressure ranges. Obviously, any other type of moisturesensor/detector could be used without departing from the scope of thepresent invention.

[0063] An electronic circuit means, preferably a microprocessor 24 orthe like digital processor, is electrically connected to the moisturedetectors 22, 22 a and the temperature detector 20. The microprocessor24 has the known water solubility properties of both the paper 12 andthe oil 14, the oil gas content level and the enclosure pressure relateddata stored therein.

[0064] Also, the microprocessor is electrically connected to adisplaying means, or display 26 of any conventional type, to display anyinformation and/or data useful to the operator or user.

[0065] Before calculating the paper moisture content level, themicroprocessor 24 compares the first and second oil moisture contentlevels to determine a relative difference between the two, with respectto the first moisture content level. This relative difference is thencompared to a predetermined value set at a reasonable level above whicha recalibration of the moisture content detectors 22, 22 a might berequired due to a divergence of their performances, thereby enabling thedetection of possible malfunction of the device 10, i.e. the first fluidmoisture content detector 22 (and similarly the first fluid temperaturedetector 20). The predetermined value is preferably set within the rangevarying between fifteen (15) and twenty-five (25) percent, preferably attwenty (20) percent. Similar validation process could be performed forthe oil temperature level using both first and second oil temperaturedetectors 20, 20 a.

[0066] Accordingly, the microprocessor 24 displays either a warningmessage or the like on the display 26 when the above calculated relativedifference is equal or larger than the predetermined value or the papermoisture content level (in percent (%)) when the calculated relativedifference is smaller than the predetermined value. Obviously, otherdata such as the first oil moisture content level (in percent (%) and/orparts per million (ppm)), oil temperature and the bubble formationtemperature could also be provided on the display 26. The calculatedpaper moisture content level is determined by the microprocessor 24 thatprocesses both the first oil moisture content level of the firstmoisture detector 22 and the oil temperature level of the temperaturedetector 20 according to an algorithm that preferably takes into accountof the location of the sensing probe 18 within the transformer alongwith the physical characteristics (windings, dimensions, power capacity,etc.), of the transformer and the power losses of the transformer.Similarly, the calculated bubble formation temperature is determined bythe microprocessor 24 that processes the paper moisture content level,the oil gas content level and the enclosure pressure related dataaccording to an algorithm that preferably takes into account of thelocation of the sensing probe 18 within the transformer along with thephysical characteristics (windings, dimensions, power capacity,geographic location, etc.), of the transformer and the power losses ofthe transformer. - There is no need to have a specific sensor formeasuring the gas content of the oil since this value do not changesignificantly over an extended period of time such as a few years.Although not required, there could be a specific pressure sensor formeasuring the pressure inside the enclosure 16 connected to themicroprocessor 24 since this value can change significantly over arelatively short period of time such as a few hours, especially forsealed-type enclosures 16. Accordingly, the device 10 includes apressure measuring means, or sensor 23, for measuring the pressure levelwithin the enclosure 16, the electronic circuit means 23 is electricallyconnected to the enclosure pressure sensor 23.

[0067] Eventually, the microprocessor 24 could display a visual alarmand/or play an audible alarm when a bubble formation temperature alarmset point that can be set-up to a preset alarm value has been reached,depending on the type of display 26 or peripheral devices connectedthereto. Similarly, a paper moisture content alarm set point could beset by the user/operator.

[0068] Although not required, the device 10 preferably includes anoperator interfacing means, or keypad 28 and the like, for an operatorto interface with the microprocessor 24. The keypad 28, electricallyconnected to the microprocessor 24, can for example allow the operatorto select the specific dielectric fluid among a fluid selection menuprovided by the microprocessor 24 on the display 26, the oil gas contentlevel and the enclosure pressure related data (preferably provided withthe keypad 28), the water solubility properties of each fluid beingalready stored into the microprocessor 24, or any conventionalperipheral component connected thereto. Alternatively, the operatorcould select a new fluid and provide its water solubility properties tothe microprocessor 24 via the keypad 28.

[0069] Similarly, a solid material selection menu could be consideredfor the different most widely used insulation papers.

[0070] Furthermore, it is well known in the art of high voltagetransformers that the temperature and the moisture content of the oil 14vary with its location within the transformer. Accordingly, themicroprocessor 24 could also provide a probe location menu through thedisplay 26 so as to allow an operator to select a specific location ofthe probe 18 containing the moisture detectors 22, 22 a and thetemperature detector 20 within the enclosure 16 via the keypad 28; thespecific location obviously affecting the determination of the soliddielectric material moisture content level and the bubble formationtemperature by the microprocessor 24.

[0071] Depending on the specific location of the probe 18, more that oneprobe 18′, 18″ connected to a same microprocessor 24 can be preferred,as illustrated in FIG. 3 by the alternate probes 18′, 18″ located atboth the inlet 38 (upstream) and the outlet 40 (downstream) of an oilfiltering unit 30 used to dry and clean the oil 14 of the transformer.

[0072] Although only the inlet alternate probe 18′ is sufficient for thedetermination of the paper moisture content level, the outlet alternateprobe 18″ is used to simultaneously monitor the operation and assess thesaturation state of an oil dryer-filter 34, or functioning state of anytype of water extraction apparatus (including vacuum type apparatuses),located between the filtering unit inlet 38 and outlet 40. Accordingly,two generally identical oil moisture content levels detected from bothprobes 18′, 18″, or water concentrations calculated therefrom, within afilter predetermined value of about between two (2) and fifteen (15)percent, and more preferably five percent (5%), when relatively comparedto each other by the microprocessor 24, indicate that the oil filter 34is saturated, or malfunctioning, since no change occurred to the oilflowing through the filter 34 (no more detectable drying-filteringaction). It is important to note that the water concentration iscalculated from the measured moisture content level and the measuredtemperature level.

[0073] Alternatively, two moisture content levels from both probes 18′,18″ slightly differing from each other, beyond preferably five percent(5%), indicate that the oil filter 34 is not saturated yet, or properlyfunctioning, since some detectable oil drying-filtering action occurredto the oil 14 between the two probes 18′, 18″. It is obvious that thesmaller the filter predetermined value is the more accurate theassessment is, as long as the measurement accuracy of the moisturedetectors 22′, 22″ of the probes 18′, 18″ permits such a smaller filterpredetermined value. This is also an important factor that the oilfilter 34 be active and properly operating to increase the life durationof the transformer and maintain its overload capacity.

[0074] Typically the dryer-filter 34, or the filter unit 30, includes afluid flowrate measuring means, preferably a volumetric pump 36 locatedupstream of the dryer-filter 34, for measuring the flowrate of the oil14 flowing through the dryer-filter 34. Obviously, any other type offluid flow meter, either built-in the filter 34 or not, could be usedwithout departing from the scope of the present invention. As shown inlong dashed lines in FIG. 3, the pump 36 is electrically connected tothe microprocessor 24 for the latter to calculate a water extractingrate of the dryer-filter 34 using the flowrate of the pump 36 with theupstream and downstream moisture content levels and temperature levelsmeasured by the moisture detectors 22′, 22″ and the temperaturedetectors 20, so as to allow an assessment of the operation of thedryer-filter 34 by the device 10.

[0075] Preferably, the microprocessor 24 includes a time register 42which is reset to zero (0) upon cleaning or replacement of thedryer-filter 34. The microprocessor 24 computes a total amount of waterextraction since the reset of the time register 42 (or lastmaintenance/replacement of the dryer-filter 34) from the calculatedwater extracting rate of the dryer-filter 34.

[0076] Any information calculated or nor, such the filter warningmessage, the water extracting rate and/or the total amount of waterextraction can be displayed on the display 26.

[0077] The microprocessor 24 typically provides a dryer-filter menuthrough the operator interfacing means so as to allow the operator toenter a water extraction capacity of the dryer-filter 34 and a flowrateassociated with the pump 36 or the like to the microprocessor 24 throughthe keypad 28. Consequently, the microprocessor 24 compares thecalculated total amount of water extraction to the water extractioncapacity in order to provide an assessment of the operation of thedryer-filter 34 by providing the operator with a general remaining timeon the display 26 before the next cleaning or replacement of thedryer-filter 34 is required.

[0078] As it would be obvious to one skilled in the art, themicroprocessor 24 can be electrically connected to a remote unit 32 suchas a conventional main computer, a handheld computer, laptop computer orthe like, preferably having its own display and keypad, used topost-process the data (oil moisture content level, oil temperature leveland/or paper moisture content level) obtained from at least one probe 18connected to one or more microprocessor circuits 24, from a same ordifferent transformers. Post-processing includes here any type ofconventional post-processing form and/or further algorithmiccalculation, usually time-consuming, to determine real-time overloadcapacity of the transformer(s) from evaluation of paper moisture contentlevels at different critical areas of the transformer(s).

[0079] The probes 18 of the device 10 of the present invention can beeither installed during manufacturing of the transformers or retrofittedin existing transformers. Accordingly, the location of these probes 18could eventually be relatively inaccessible to an operator. Therefore,all electrical connections described hereinabove between the differentcomponents could be remote or wireless type connections withoutdeparting from the scope of the present invention, as illustrated inshort dashed lines in FIGS. 1 and 3, although the physical electricallinks are preferred for reliability purposes.

[0080] The present invention also refers to a method for monitoringmoisture content of a solid dielectric material 12 immersed in adielectric fluid 14 inside an enclosure 16 and a corresponding bubbleformation temperature within the enclosure 16, as schematicallyrepresented by the flow diagrams of FIGS. 2 and 2a. The method comprisesthe following steps of:

[0081] a) measuring moisture content level of the dielectric fluid, oroil 14, using a moisture detector 22;

[0082] b) measuring temperature level of the oil 14 using a temperaturedetector 20; and

[0083] c) computing the solid dielectric material moisture level and thecorresponding bubble formation temperature using an electronic circuitor microprocessor 24, the latter being electrically connected to boththe moisture detector 22 and the temperature detector 20.

[0084] The method preferably includes the step of:

[0085] d) displaying the solid dielectric material moisture contentlevel and the corresponding bubble formation temperature using thedisplay 26.

[0086] In the method, the step a) could include the measurement of asecond moisture content level of the oil 14 using a second moisturedetector 22 a. Step c) includes the comparison of the first and seconddielectric fluid moisture content levels and the calculation of arelative difference there between, relative to the first dielectricfluid moisture content level. And the following step:

[0087] d) displaying on the display 26 either a warning message when therelative difference is equal or larger than the predetermined valuehereinabove described or the solid dielectric material moisture contentlevel and the corresponding bubble formation temperature when therelative difference is smaller than the predetermined value.

[0088] Alternatively, in the method, the step b) could include themeasurement of a second temperature level of the oil 14 using a secondtemperature detector 20′. Step c) includes the processing of the firstand second fluid temperature levels and the fluid moisture content levelso as to determine first and second solid dielectric material moisturecontent levels respectively. And the following step:

[0089] d) displaying on the display 26 either an average of the firstand second solid dielectric material moisture content levels and thecorresponding bubble formation temperature.

[0090] Alternatively, as illustrated by dashed connecting lines in FIG.2, the method could include the step of:

[0091] d) sending the solid dielectric material moisture level to aremote unit 32, such as a micro-computer, a handheld computer or thelike, so as to allow post-processing thereof; the computer device iselectrically connected to the microprocessor.

[0092] Optionally, the method includes after step b) the step of:

[0093] b1) providing an operator interface or keypad 28 so as to allowthe operator to interface with the microprocessor 24, possibly via aremote unit or handheld computer 32 connected thereto, and eitherperform a selection of the paper material 12 and/or oil 14 among amaterial selection menu provided by the microprocessor 24 on the display26 or enter the known water solubility properties of a new papermaterial 12 and/or oil 14 present in the transformer, the oil gascontent level and the enclosure pressure related data.

[0094] Similarly, step b1) could allow an operator to select a specificlocation of the probe 18 within the enclosure 16 among a detectorlocation menu provided by the microprocessor 24 on the display 26through the keypad 28.

[0095] Especially when the enclosure 16 is a sealed-type enclosure, stepa) includes measuring a pressure level of the enclosure 16 using apressure sensor 23; and step c) includes the electronic circuit 24 beingelectrically connected to the pressure sensor 23.

[0096] As illustrated in FIG. 3, when the probe 18′ is located upstreamof the dryer-filter .34, it could simultaneously be used, in conjunctionwith a second probe 18″ located downstream of the dryer-filter 34, tomonitor the operation of the latter.

[0097] Obviously, one skilled in the art would understand that the stepsreferring to a measurement do not have a specific order and couldultimately all be performed simultaneously without departing from thescope of the present invention.

[0098] Accordingly, as illustrated in the schematic flow diagram of FIG.4, the method for monitoring the operation of the oil dryer-filter 34comprises the following steps of:

[0099] measuring a first inlet moisture content level of the oil 14upstream of the oil dryer-filter 34 using an inlet moisture detector22′;

[0100] measuring a second outlet moisture content level of the oil 14downstream of the oil dryer-filter 34 an outlet moisture detector 22″;and

[0101] computing a filter relative difference between the first andsecond dielectric fluid moisture content levels relative to the firstdielectric fluid moisture content level using a microprocessor 24. Thelatter is electrically connected to both first and second moisturedetectors 22′, 22″ and provides a filter warning message when the filterrelative difference is equal or smaller than a filter predeterminedvalue;

[0102] whereby the method enables detection of saturation ormalfunctioning state of the dryer-filter 34.

[0103] Optionally, the dryer-filter 34 includes a fluid flowratemeasuring means, or volumetric pump 36, electrically connected to themicroprocessor 24 to measure the flowrate of oil 14 flowing through thedryer-filter 34, and the method further includes the step of:

[0104] measuring a first temperature level of the oil 14 upstream of thefluid dryer-filter 34 using a first temperature detector 20;

[0105] measuring a second temperature level of the oil 14 downstream ofthe fluid dryer-filter 34 using a second temperature detector 20;

[0106] computing a water extracting rate of the dryer-filter 34 with themicroprocessor 24 using the flowrate of the oil 14, the first and secondmoisture content levels and the first and second temperature levels, themicroprocessor 24 being electrically connected to the pump 36 and thefirst and second temperature detectors 20; whereby the method allows forassessment of the operation of the dryer-filter 34.

[0107] Also, the microprocessor 24 includes a time register 42, and themethod further includes the steps of:

[0108] resetting the time register 42 to zero (0) upon cleaning orreplacement of the dryer-filter 34; and

[0109] computing a total amount of water extraction since resetting ofthe time register 42 from the water extracting rate of the dryer-filter34.

[0110] Typically, the method includes the step of providing an operatorinterface, or keyboard 28/display 26, electrically connected to themicroprocessor 24 for an operator to interface therewith. Themicroprocessor 24 provides a dryer-filter menu through the display 26 soas to allow an operator to provide the microprocessor 24 with a waterextraction capacity of the dryer-filter 34 and a flowrate of the pump36. The microprocessor 24 compares the total amount of water extractionto the water extraction capacity to determine assessment of the properoperation of the dryer-filter 34 and to provide the operator with ageneral remaining time on the display 26 before a next cleaning orreplacement of the dryer-filter 34 is required.

[0111] The above description always refers to the first oil moisturecontent level being used in the calculation of the paper moisturecontent level when two moisture detectors 22, 22 a are present in theprobe 18, but the second oil moisture content level, or either anaverage of the two, can be used in the calculation of the paper moisturecontent level without departing from the scope of the present invention.Similarly, when two probes 18, 18′ located in different regions of thetransformer (such as top and bottom regions of the enclosure 16 as shownin FIG. 1, or the like) are considered, the paper moisture content levelcould be an average of first and second paper moisture content levelsdetermined from either first and second oil moisture content levelsobtained from first and second oil moisture detectors 22′, 22″ and thefirst and second oil temperature levels obtained from correspondingfirst and second oil temperature detectors 20 respectively, or the oilmoisture content level obtained from the oil moisture detector 22 andthe first and second oil temperature levels obtained from first andsecond oil temperature detectors 20, 20′, respectively. Typically, thebubble formation temperature assessment is performed for the insulationpaper 12 located adjacent one third of the transformer enclosure 16height below the top region, although it could be performed for anyother location therein.

[0112] Although not specified hereinabove, the device 10 preferablycontinuously monitors the paper moisture content level, many times perseconds, any monitoring rate could be considered depending on thespecific need of the operator and without departing from the scope ofthe present invention.

[0113] Although the present method and/or device for monitoring moisturerelated operating condition of an immersed solid dielectric materialhave been described with a certain degree of particularity, it is to beunderstood that the disclosure has been made by way of example only andthat the present invention is not limited to the features of theembodiments described and illustrated herein, but includes allvariations and modifications within the scope and spirit of theinvention as hereinafter claimed.

I claim:
 1. A device for monitoring moisture content level of a soliddielectric material inside an enclosure and a corresponding bubbleformation temperature within the enclosure, said solid dielectricmaterial being immersed in a dielectric fluid, said dielectric fluidfilling said enclosure, said solid dielectric material and saiddielectric fluid having a respective moisture content, said soliddielectric material and said dielectric fluid having known watersolubility properties varying with temperature thereof, said dielectricfluid having a gas content level thereof, said enclosure having pressurerelated data thereof, said device comprising: a moisture measuring meansfor measuring moisture content level of said dielectric fluid; atemperature measuring means for measuring temperature level of saiddielectric fluid; and an electronic circuit means for computing saidmoisture content level of said solid dielectric material and saidcorresponding bubble formation temperature, said electronic circuitmeans being electrically connected to both said moisture measuring meansand said temperature measuring means, said electronic circuit meanshaving said known water solubility properties of said solid dielectricmaterial and said dielectric fluid stored therein, said electroniccircuit means processing said fluid moisture content level and saidfluid temperature level so as to determine said solid dielectricmaterial moisture content level and said bubble formation temperatureusing said solid dielectric material moisture content level, thedielectric fluid gas content level and the enclosure pressure relateddata.
 2. The device of claim 1, wherein said electronic circuit meansincludes a displaying means for displaying said solid dielectricmaterial moisture content level and said corresponding bubble formationtemperature, said displaying means being electrically connected to saidelectronic circuit means.
 3. The device of claim 1, including anoperator interfacing means for an operator to interface with saidelectronic circuit means, said operator interfacing means beingelectrically connected to said electronic circuit means so as to allowsaid known water solubility properties of said solid dielectric materialand said dielectric fluid, the dielectric fluid gas content level andthe enclosure pressure related data to be provided to and stored in saidelectronic circuit means.
 4. The device of claim 1, wherein saidelectronic circuit means is remotely electrically connected to both saidmoisture measuring means and said temperature measuring means so as toallow said moisture measuring means and said temperature measuring meansto be located in a generally inaccessible location.
 5. The device ofclaim 1, including an operator interfacing means for an operator tointerface with said electronic circuit means, said operator interfacingmeans being electrically connected to said electronic circuit means,said electronic circuit means providing a sensor location menu throughsaid operator interfacing means so as to allow an operator to select aspecific location of both said moisture measuring means and saidtemperature measuring means within said enclosure, whereby said specificlocation affecting determination of said solid dielectric materialmoisture content level and said corresponding bubble formationtemperature by said electronic circuit means.
 6. The device of claim 2,including: a second moisture measuring means for measuring secondmoisture content level of said dielectric fluid, said electronic circuitmeans comparing said first and second dielectric fluid moisture contentlevels and calculating a relative difference therebetween relative tosaid first dielectric fluid moisture content level, said electroniccircuit means displaying on said displaying means either a warningmessage when said relative difference is equal or larger than apredetermined value or said solid dielectric material moisture contentlevel and said corresponding bubble formation temperature when saidrelative difference is smaller than said predetermined value; wherebysaid second moisture measuring means being a reference moisturemeasuring means to enable detection of malfunction of said device. 7.The device of claim 2, including: a second temperature measuring meansfor measuring second moisture temperature level of said dielectricfluid, said electronic circuit means processing said first and secondfluid temperature levels and said fluid moisture content level so as todetermine first and second solid dielectric material moisture contentlevels respectively, said electronic circuit means displaying on saiddisplaying means an average of said first and second solid dielectricmaterial moisture content levels and said corresponding bubble formationtemperature.
 8. The device of claim 7; wherein said first and secondtemperature measuring means are located adjacent bottom and top regionsof the enclosure, respectively.
 9. The device of claim 2, including: asecond moisture measuring means for measuring second moisture contentlevel of said dielectric fluid, said electronic circuit means comparingsaid first and second dielectric fluid moisture content levels andcalculating a relative difference therebetween relative to said firstdielectric fluid moisture content level, said electronic circuit meansprocessing said first and second fluid moisture content levels and saidfluid temperature level so as to determine first and second soliddielectric material moisture content levels respectively, saidelectronic circuit means displaying on said displaying means either awarning message when said relative difference is equal or larger than apredetermined value or an average of said first and second soliddielectric material moisture content levels and said correspondingbubble formation temperature when said relative difference is smallerthan said predetermined value; whereby said second moisture measuringmeans being at least a reference moisture measuring means to enabledetection of malfunction of said device.
 10. The device of claim 1,wherein the pressure related data includes a pressure level within theenclosure, and wherein said device further includes a pressure measuringmeans for measuring pressure level within the enclosure, said electroniccircuit means being electrically connected to said pressure measuringmeans.
 11. A method for monitoring moisture content level of a soliddielectric material inside an enclosure and a corresponding bubbleformation temperature within the enclosure, said solid dielectricmaterial being immersed in a dielectric fluid, said dielectric fluidfilling said enclosure, said solid dielectric material and saiddielectric fluid having a respective moisture content, said soliddielectric material and said dielectric fluid having known watersolubility properties varying with temperature thereof, said dielectricfluid having a gas content level thereof, said enclosure having pressurerelated data thereof, said method comprising the following steps: a)measuring moisture content level of said dielectric fluid using amoisture detector; b) measuring temperature level of said dielectricfluid using a temperature detector; and c) computing said soliddielectric material moisture content level and said corresponding bubbleformation temperature using a processor electronic circuit, saidelectronic circuit being electrically connected to both said moisturedetector and said temperature detector, said electronic circuit havingsaid known water solubility properties of said solid dielectric materialand said dielectric fluid stored therein, said electronic circuitprocessing said fluid moisture content level and said fluid temperaturelevel so as to determine said solid dielectric material moisture contentlevel and said bubble formation temperature using said solid dielectricmaterial moisture content level, the dielectric fluid gas content leveland the enclosure pressure related data.
 12. The method recited in claim11., including the step of: d) displaying said solid dielectric materialmoisture level and said corresponding bubble formation temperature usinga display, said display being electrically connected to said electroniccircuit to receive said solid dielectric material moisture content leveland said corresponding bubble formation temperature therefrom.
 13. Themethod recited in claim 12, wherein said display is remotelyelectrically connected to said electronic circuit.
 14. The methodrecited in claim 12, wherein step a) includes measuring a secondmoisture content level of said dielectric fluid using a second moisturedetector; step c) includes said electronic circuit comparing said firstand second dielectric fluid moisture content levels and calculating arelative difference therebetween relative to said first dielectric fluidmoisture content level; and step d) includes displaying on said displayeither a warning message when said relative difference is equal orlarger than a predetermined value or said solid dielectric materialmoisture content level and said corresponding bubble formationtemperature when said relative difference is smaller than saidpredetermined value; whereby said second moisture detector being areference moisture detector to enable detection of malfunction of saidfirst moisture detector.
 15. The method recited in claim 12, whereinstep b) includes measuring a second moisture content level of saiddielectric fluid using a second moisture detector; step c) includes saidelectronic circuit processing said first and second fluid temperaturelevels and said fluid moisture content level so as to determine firstand second solid dielectric material moisture content levelsrespectively; and step d) includes displaying on said display an averageof said first and second solid dielectric material moisture contentlevels and said corresponding bubble formation temperature.
 16. Themethod recited in claim 15, wherein said first and second temperaturedetectors are located adjacent bottom and top regions of the enclosure,respectively.
 17. The method recited in claim 11, including the step of:d) sending said solid dielectric material moisture content level andsaid corresponding bubble formation temperature to a remote unit so asto allow post-processing thereof, said remote unit being electricallyconnected to said electronic circuit.
 18. The method recited in claim11, including after step b) the step of: b1) providing an operatorinterface so as to allow said known water solubility properties of saidsolid dielectric material and said dielectric fluid, the dielectricfluid gas content level and the enclosure pressure related data to beprovided therethrough; said operator interface being electricallyconnected to an electronic circuit for an operator to interfacetherewith and store said known water solubility properties of said soliddielectric material and said dielectric fluid, the dielectric fluid gascontent level and the enclosure pressure related data therein.
 19. Themethod recited in claim 18, wherein said operator interface is remotelyelectrically connected to said electronic circuit.
 20. The methodrecited in claim 11, including after step b) the step of: b1) providingan operator interface electrically connected to an electronic circuitfor an operator to interface therewith, said electronic circuitproviding a detector location menu through said operator interface so asto allow an operator to select a specific location of both said moisturedetector and said temperature detector within said enclosure, wherebysaid specific location affecting determination of said solid dielectricmaterial moisture content level and said corresponding bubble formationtemperature by said electronic circuit.
 21. The method recited in claim12, wherein step a) includes measuring a second moisture content levelof said dielectric fluid using a second moisture detector; step c)includes said electronic circuit comparing said first and seconddielectric fluid moisture content levels and calculating a relativedifference therebetween relative to said first dielectric fluid moisturecontent level, said electronic circuit processing said first and secondfluid moisture content levels and said fluid temperature level so as todetermine first and second solid dielectric material moisture contentlevels respectively; and step d) includes displaying on said displayeither a warning message when said relative difference is equal or anaverage of said first and second solid dielectric material moisturecontent levels and said corresponding bubble formation temperature whensaid relative difference is smaller than said predetermined value;whereby said second moisture detector being at least a referencemoisture detector to enable detection of malfunction of said firstmoisture detector.
 22. The method recited in claim 11, wherein thepressure related data includes a pressure level within the enclosure,and wherein step a) includes measuring a pressure level of the enclosureusing a pressure sensor; step c) includes said electronic circuit beingelectrically connected to said pressure sensor.